Various cleansing blocks for use in toilet tanks and other water reservoirs are known. Such cleansing blocks typically contain a surfactant for cleaning, and often oxidizing agents, fillers, binders, colorants and perfumes. They are designed to slowly release these materials into the toilet basin each time the toilet is flushed. See e.g. U.S. Pat. Nos. 4,269,723; 4,722,801; 4,722,802; 4,738,728; 4,820,449; 5,336,427; and 5,449,473. The disclosure of these patents, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein.
Such blocks should not include materials which leave undesirable residues in the toilet bowl, which are environmentally unacceptable, or which have unpleasant odors. While blocks having these desired attributes have been created, there are sometimes unsatisfactory trade-offs between desired attributes for each formulation.
As useful life is extended, it is particularly difficult to insure consistent performance independent of water hardness or softness. Variations in the hardness of the water supply can affect the rate of dissolution, especially when the block is designed for very long life. The consumer dissatisfaction associated with inconsistent performance is increasingly of concern as more and more people use softened water or move to soft water areas.
Thus, it can be seen that a need exists for an improved water tank cleansing block.